Failure to maintain adequate and stable fuel rail pressure by fuel pumps installed in fuel injected IC engines can result in poor or erratic fuel injector performance and inefficient engine performance. Conventional test methods are cumbersome and time consuming, some requiring the pump to be removed from the engine and bench tested. Moreover, low fuel rail pressure can be caused not only by a defective or degraded pump, but also by excessive leakage from the fuel rail during engine operation. Consequently, a diagnostic procedure with the pump installed ideally should allow the test operator to determine if one or more of the pump pumping elements is the cause of poor performance rather than, or in addition to, excessive rail leakage.
Methods for testing installed fuel supply systems are known but are relatively complex or do not provide quantitative results. For example, EP 0 501 459 discloses a method detecting pump-abnormality or failure by monitoring and tracing the output signal from a common rail pressure sensor to detect a rail pressure variation pattern (i.e., pressure vs. time curve). The curve is then compared with patterns/curves corresponding to normal pump operation to detect pump-abnormality/failure. For multiple pumps, the method alternatively suspends operation in the other pump when the pressure curve for one pump is being recorded. EP 0 501 459 also discloses that the pump failure detecting method can be provided in a program installed in a vehicle's electronic control unit (“ECU”).
U.S. Pat. No. 5,708,202 to Augustine et al. discloses a method for testing for unacceptable leakage in a fuel injection system installed on an IC engine. The method includes measuring pressure in the common fuel rail at two points in time between a fuel injection event and an immediately prior or subsequent pump delivery event. Any difference in measured pressure such as due to system fuel leakage is compared with a predetermined acceptable threshold value. If the pressure difference exceeds the threshold, an “operating error” is indicated. The method also contemplates switching off momentarily at least one of successive fuel injection events and pump delivery events, to detect small leakage volumes. Further, the leakage detection method may be accomplished using the engine ECU to momentarily switch off the selected injector and pump delivery events.